Thalidomide-O-PEG4-NHS ester is widely used in the development of PROTACs (Proteolysis Targeting Chimeras), a cutting-edge technology in drug discovery. It serves as a key linker component, enabling the targeted degradation of specific proteins by recruiting E3 ubiquitin ligases. This compound is particularly valuable in cancer research, where it helps degrade oncogenic proteins that are otherwise difficult to target with traditional inhibitors. Additionally, it is employed in the design of bifunctional molecules for studying protein-protein interactions and cellular pathways. Its PEG4 spacer enhances solubility and stability, while the NHS ester group allows efficient conjugation to amine-containing molecules, making it a versatile tool in chemical biology and therapeutic development.